Boom constructions or assemblies on trucks and other vehicles generally have at least two boom arms flexibly connected to each other by an articulated joint via a swivel axis are utilized for various working devices such as excavators. One application is with concrete pumps, whether stationary or mobile, such as truck-mounted concrete pumps. In this application, the boom arms carry concrete delivery lines to discharge the concrete at desired locations. On construction of the building structure, the individual boom arms can be extended by swiveling, resulting in a change of the boom geometry and thus making it possible to reach different locations on site through the boom. With a boom, concrete can be delivered relatively large distances, for example, from the concrete pump to the place of pouring the concrete on construction site. On account of the large range of the boom, it is subjected to significant loads which essentially originate from the concrete-carrying delivery line running the length of the boom and from the concrete carried therein.
When used in conjunction with truck-mounted concrete pumps, it is not allowed to exceed the load limits of the relevant vehicle types, which in most cases are vehicles admitted for traffic on public roads, in particular trucks. While the masses of the delivery lines of concrete can hardly be influenced, if at all, achieving a greater range of the boom calls for optimizing its masses.
The articulated joints between the boom arms are exposed to high requirements. To obtain a sufficiently powerful drive, coupler gear mechanisms in the kind of double-acting hydraulic cylinders, so-called thrust piston gears are mostly utilized for the swiveling motion. However, due to the components of the coupler gear mechanisms and the linear drive units associated therewith, they have a relatively heavy weight and call for substantial space which is due to their construction style. But this is problematic because such truck-mounted concrete pumps are mounted on vehicles which have to be licensed for operation in road traffic and therefore are subject to certain codes and rules with regard to their width and length. Furthermore, thrust piston gears applied here have a disadvantage in that the angular velocity during the swiveling motion is relatively uneven. Therefore, to ensure safe operation of this boom construction, the use of hydraulic load holding valves at the hydraulic cylinders is mandatory, because their yielding would cause an impermissible change of the rotary angle between the boom arms. Add to this that for such coupler gear mechanisms in the kind of thrust piston gears, even the swiveling of the two boom arms towards each other is only feasible in restricted extent, thus prompting a limitation in the effect and function.
Since with multiple-arm boom constructions, the predominant load in the last boom arms is usually less than in the first boom arms, even hydraulic rotary drives (DE 698 01 997 T1) are in some cases used at the articulated joints towards the boom end in prior art as an alternative to the kinematic system described before, whereby it is possible to achieve uniform angular velocities. Though these means are relatively small in size and thus lighter in weight as compared to coupler gear mechanisms and/or thrust piston gears, but the required driving moments are not available that are needed for swiveling the articulated joints of boom arms in the lower boom area, too. Besides, when applying such hydraulic rotary drives for load pick-up devices such as hinged arms of manipulators, boom arms and the like, the problem arises in that the load pick-up device and/or the boom arm when deactivating the rotary drive due to a leakage, for example, still stays rotatable and can swivel and/or pivot. However, as has been outlined hereinabove, such a twisting with a deactivated drive is impermissible with these applications, in particular for truck-mounted concrete pumps, which is the reason why in prior art appropriate braking devices are used on rotary drives, for example multiple disk brakes, in order to prevent twisting of the boom arms in case of a deactivated rotary drive. With such multiple disk brakes, lamella-like brake disk pairs are pressed against each other to prevent a twisting of the boom arms relatively to each other, these parts here being real wear parts. It is also known from prior art realizing a brake by preventing the flow-off of hydraulic fluid from at least one pressure chamber by means of separate shutoff devices. However, those measures are comparably costly and susceptible to faults.
Finally, U.S. Pat. No. 4,771,646A discloses a device by way of which a rotary motion can be generated. Accordingly, a component hydraulically moved back and forth is so guided by a journal and sprocket assembly that a rotation motion is developed.